Some grubs can cause massive damage and destroy entire lawns. Find out how to effectively combat the beetle larvae in this article.
The larvae of many beetle species are called grubs. The larvae of the common cockchafer (Melolontha melolontha), the June bug (Amphimallon solstitiale) and the garden chafer (Phyllopertha horticola) are also referred to as grubs. All three belong to the scarab beetle family (Scarabaeidae) and can cause great damage to domestic lawns. However, there are also beneficial insects among the grubs of this beetle family, some of which are even officially protected. We will tell you how to recognise the pests among the grubs and how to get rid of them.
Identifying grubs: Characteristics
It is important that you first correctly identify the harmful grubs. Each species has distinctive characteristics that make the identification possible. The following guide will help you to correctly pinpoint the unwelcome guests in your garden and discern them from insects that are beneficial and should be kept unharmed.
The larva of the May bug or the cockchafer grows up to 4 cm long. Its expected lifespan averages between three and four years. The cockchafer grub is shaped relatively evenly over the entire body and has a slightly yellowish colouring. Depending on the stage of development, this colour may darken a little (towards the brownish side). The grub of the cockchafer is characterized by the strong mandibles (mouth parts) and leg pairs at the front half of the body.
The grubs of the June beetle look very similar to those of the May beetle, only slightly smaller. To some, they may seem indistinguishable from one another. The so-called ‘movement test’ should also help the untrained eye to distinguish the grubs of the two species. If the larva is placed on its back on a smooth surface (for example the pavement), then one can distinguish which type of bug it is by how the grub moves. The cockchafer grub is supposed to curl sideways in a curved position. The larvae of the June bug, on the other hand, should stretch and then try to crawl.
The grubs of the garden chafer are not as uniformly shaped as those of the May and June beetles. While they are rather narrow in the front body, their hind body is thicker with the increasing length. They are bright white in colour, but sometimes have greyish shades. Their mouth parts and legs appear rather small, but are all the stronger. In the movement test, the grub of the garden chafer is conspicuous because of its caterpillar-like movements.
Attention: It is essential that you identify your grubs before taking any action. The grubs may also be the larvae of the European rhinoceros beetle (Oryctes nasicornis). This is a beneficial animal and is in fact a protected species.
Grubs in the lawn: symptoms of damage
The most obvious sign of a grub infestation is an extensive dying off of the lawn. Note: the dead patches of lawn can of course also have other causes, which is why you should look for further evidence. Simply dig up a small part of the dead lawn area and search the excavated area for larvae.
The grubs move a few centimetres underground and feed on rotting but also fresh plant material. It can happen, for example, that entire swards of grass are damaged during a severe infestation. What remains is a brown dry area.
Successfully combating grubs in the lawn
Grub outbreaks can be prevented well with planting discs. Planting discs are ground-covering, mostly round plastic plates which lie freely in the ground. Simply plant them below ground cover plants. The most effective way is to promote the habitat of the natural predators of the grubs in your own garden. A cosy and somewhat unkept corner in the garden attracts hedgehogs and birds, who will then willingly take care of the grub plague.
Controlling grubs with nematodes
In a case of an acute infestation, however, the methods mentioned above do not really help. Nematodes are the most effective method of eliminating grubs.
Nematodes are tiny beneficial organisms that parasitize and kill the larvae of the beetles. But beware: the small helpers can only be used effectively during young larval stages of the grubs. In later phases of the beetle life, the nematode efficiency drops sharply.
In addition, care must be taken to select the correct nematode species so that this method can actually work. Nematode populations of Heterorhabditis and Steinernema have proven to be an effective mixture. You should also note that the environmental conditions are optimal for the use of nematodes. The temperatures must in any case be above 12 °C and it should not be too humid.
The microscopically small nematodes are available in well-stocked specialist shops and are spread using water in a can. The nematodes multiply in the soil, attack the grubs and, as a result, kill them.
If you would like to find out more about nematodes for pest control, read on here.